Capabilities and performance of the wavefront-based alignment in multi element optical systems

The complexity of optics manufacturing is not only due to the demanding geometrical features of single surfaces, it increases significantly when several surfaces need to be aligned in the correct position within a multi element optical system. Even slight imperfections of this alignment process in the range of a few microns can lead to a substantially reduced quality of the overall system. The functional orientated wavefront based alignment approach offers an elegant solution to this challenge. Compared to conventional alignment methods it has the potential to reach very high accuracies in the sub-μm-range with an excellent efficiency. A consecutive stepping through the system is not necessary, since after the measurement of the optical performance of the system the correction of all possible degrees of freedom will be calculated at the same time. In order to transfer this potential into real applications two major challenges related to the available measurement devices have to be met. The first one is the repeatability of the wavefront measurement. Tiny errors in the position lead to also quite small changes in the wavefront properties which need to be detected reliable. The other aspect concerns the limited sensor area of real measurement devices. Depending on the magnitude of the perturbation in the different degrees of freedom the lateral displacement of the resulting spot is generally a lot larger the sensor area available. Therefore, this publication will initially introduce to the capabilities of the wavefront based alignment approach, illustrating the performance and accuracies as well as some of the parameters decisive to the procedure. Furthermore this paper will elaborate on the mentioned challenges in the transfer of these results to real applications